From the BBC -- How computers took over our cars

[Blue_Tires]

Toyota's recall of its Prius model this week wasn't down to a mechanical fault but a software glitch. Increasingly, computers are in control of our cars, says Paul Horrell, and that is changing our relationship with the open road.

In this week's recall of the Toyota Prius, there is no faulty mechanical component. All that's necessary is a quick software update to recalibrate the electrically generated pedal "feel" in its braking system. Which just goes to show how deeply computer control is embedded in today's cars.

The Prius is such a famously economical car partly because of its regenerative braking system. When the driver touches the brake pedal, there is no mechanical link to the normal brake discs. In gentle braking, all that happens is the electric generator in the powertrain takes up the load, slowing the car by collecting its kinetic energy and re-charging its battery.

Only when the driver brakes moderately hard, or when the battery is charged, do the electronics hand over the braking effort to the wheel discs. For this to occur smoothly, instantly and predictably is an extraordinarily complex piece of control technology.

But then, while they don't have this type of "brake by wire", all modern cars do have some electronics in the brakes. The anti-lock braking system (ABS) detects if a wheel has locked up, which causes a skid. ABS corrects this by over-riding the mechanical command from the pedal, easing the braking pressure on the affected wheel.

Back in the 1980s, ABS, along with electronically regulated fuel injection, was one of the first pieces of electronics in cars. They used to be a selling point - now they're standard by law. You can't have modern exhaust emission control without fuel injection, and electronic control is nowadays cheaper and more effective than mechanical.

As cars have become more economical over the years, the degree of electronic optimisation of the engine and transmission has grown. And on hybrid cars such as the Prius and Honda Insight, it's orders of magnitude more complex again. All the driver does is press the throttle, but the powertrain electronics module independently controls both the petrol engine and the electric motor, and the transmission that blends them, to give the most economical drive at any given moment.

Many of today's computerised systems take the load off the driver, for the sake of safety or convenience. High-end cars have radar-based cruise control to vary their speed, keeping them a safe distance from the car in front. "Crash mitigation" uses the radar to sense that the car in front has stopped or there's an obstacle, and can apply the brakes if the driver fails to.

http://news.bbc.co.uk/2/hi/uk_news/magazine/8510228.stm